A central policy assumption in the U.S. today is that expanding health insurance coverage will improve access to health care, improve health outcomes, and make each more equitable for all Americans. Despite its uncertain future, the Affordable Care Act (ACA) of 2010, the most important legislation in health care since the passage of Medicare and Medicaid, holds great promise for reducing racial/ethnic disparities in healthcare access and population health. With the objective of evaluating the impact of the 2014 ACA coverage expansion on racial/ethnic disparities in healthcare access, utilization, outcomes and quality, the proposed study has three foci. First, we will examine measures based on actual healthcare inpatient and emergency department (ED) utilization. Second, to better focus on Hispanics, the largest racial/ethnic minority with higher uninsurance rate (41%) than among non-Hispanic whites (15%), non-Hispanic blacks (21%) and Asians (26%), we will develop a near-national database by combining state inpatient discharge data from 22 states that together account for over 88 percent of the national Hispanic population; corresponding ED data is available from a subset of 13 states. Third, far from being an uniform intervention, ACA expansion engendered wide variation in implementation, particularly across states; we will evaluate how reform effects among Hispanics are modified by language barriers, national origin, baseline uninsurance, state Medicaid generosity, and provider availability. To estimate changes associated with the 2014 ACA insurance expansion by race/ethnicity, we will use a difference- in-differences design, wherein pre-expansion (2010-2013) to post-expansion (2014-2017) changes in the study outcome measures are contrasted with those in a comparison cohort thatexperienced no insurance expansion. Our specific aims are to estimate the changes associated with ACA coverage expansion in rates of (1) ambulatory care sensitive condition admissions and ED visits, (2) major elective procedures, (3) inpatient mortality and 30-day readmission, and (4) use of safety-net hospitals vs. non- safety-net hospitals, and disparities in such rates by race/ethnicity. We will examine changes in outcomes among subgroups of Hispanics by English language proficiency, national origin, sex and socioeconomic status. Our proposal has unique strengths: the data used represents a near-national population of Hispanics; it delineates impact across vulnerable subgroups of Hispanics; it identifies the role of potential facilitating and inhibiting factors, such as, provider availability and state Medicaid policy.